Coke plant including exhaust gas sharing

ABSTRACT

A coke plant includes multiple coke ovens where each coke oven is adapted to produce exhaust gases, a common tunnel fluidly connected to the plurality of coke ovens and configured to receive the exhaust gases from each of the coke ovens, multiple standard heat recovery steam generators fluidly connected to the common tunnel where the ratio of coke ovens to standard heat recovery steam generators is at least 20:1, and a redundant heat recovery steam generator fluidly connected to the common tunnel where any one of the plurality of standard heat recovery steam generators and the redundant heat recovery steam generator is adapted to receive the exhaust gases from the plurality of ovens and extract heat from the exhaust gases and where the standard heat recovery steam generators and the redundant heat recovery steam generator are all connected in parallel with each other.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of coke plants forproducing coke from coal. Coke is an important raw material used to makesteel. Coke is produced by driving off the volatile fraction of coal,which is typically about 25% of the mass. Hot exhaust gases generated bythe coke making process are ideally recaptured and used to generateelectricity. One style of coke oven which is suited to recover these hotexhaust gases are Horizontal Heat Recovery (HHR) ovens which have aunique environmental advantage over chemical byproduct ovens based uponthe relative operating atmospheric pressure conditions inside the oven.HHR ovens operate under negative pressure whereas chemical byproductovens operate at a slightly positive atmospheric pressure. Both oventypes are typically constructed of refractory bricks and other materialsin which creating a substantially airtight environment can be achallenge because small cracks can form in these structures duringday-to-day operation. Chemical byproduct ovens are kept at a positivepressure to avoid oxidizing recoverable products and overheating theovens. Conversely, HHR ovens are kept at a negative pressure, drawing inair from outside the oven to oxidize the coal volatiles and to releasethe heat of combustion within the oven. These opposite operatingpressure conditions and combustion systems are important designdifferences between HHR ovens and chemical byproduct ovens. It isimportant to minimize the loss of volatile gases to the environment sothe combination of positive atmospheric conditions and small openings orcracks in chemical byproduct ovens allow raw coke oven gas (“COG”) andhazardous pollutants to leak into the atmosphere. Conversely, thenegative atmospheric conditions and small openings or cracks in the HHRovens or locations elsewhere in the coke plant simply allow additionalair to be drawn into the oven or other locations in the coke plant sothat the negative atmospheric conditions resist the loss of COG to theatmosphere.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to a coke plant includingmultiple coke ovens where each coke oven is adapted to produce coke andexhaust gases, a common tunnel fluidly connected to the plurality ofcoke ovens and configured to receive the exhaust gases from each of thecoke ovens, multiple standard heat recovery steam generators fluidlyconnected to the common tunnel where the ratio of coke ovens to standardheat recovery steam generators is at least 20:1, and a redundant heatrecovery steam generator fluidly connected to the common tunnel whereany one of the standard heat recovery steam generators and the redundantheat recovery steam generator is adapted to receive the exhaust gasesfrom the coke ovens and extract heat from the exhaust gases and wherethe standard heat recovery steam generators and the redundant heatrecovery steam generator are all fluidly connected in parallel with eachother.

Another embodiment of the invention relates to a method of operating acoke producing plant including the steps of providing multiple cokeovens to produce coke and exhaust gases, directing the exhaust gasesfrom each coke oven to a common tunnel, fluidly connecting multiple heatrecovery steam generators to the common tunnel, operating all of theheat recovery steam generators and dividing the hot exhaust gases suchthat a portion of the hot exhaust gases flows through each of the heatrecovery steam generators, and in a gas sharing operating mode, stoppingoperation of at least one of the heat recovery steam generators anddividing the exhaust gases to the remaining operating heat recoverysteam generators such that a portion of the exhaust gases flows througheach of the operating remaining heat recovery steam generators.

Another embodiment of the invention relates to a method of operating acoke producing plant including the steps of providing multiple cokeovens wherein each coke oven is adapted to produce coke and exhaustgases, providing a common tunnel fluidly connected to the coke ovens andbeing configured to receive the exhaust gases from each of the cokeoven, providing multiple standard heat recovery steam generators fluidlyconnected to the common tunnel, wherein the ratio of coke ovens tostandard heat recovery steam generators is at least 20:1, providing aredundant heat recovery steam generator and fluidly connecting theredundant heat recovery steam generator to each of the coke ovens sothat the redundant heat recovery steam generator is adapted to receiveand extract heat from the exhaust gases generated by any of theplurality of coke ovens.

Another embodiment of the invention relates to a method of operating acoke producing plant including the steps of providing multiple cokeovens wherein each coke oven is adapted to produce coke and exhaustgases, providing a common tunnel fluidly connected to the coke ovens andbeing configured to receive the exhaust gases from each of the cokeovens, providing multiple heat recovery steam generators, providingmultiple crossover ducts with each crossover duct adapted to fluidlyconnect the common tunnel to one of the heat recovery steam generatorsat an intersection, and controlling operating conditions at one or moreof the intersections to maintain an intersection draft of at least 0.7inches of water.

Another embodiment of the invention relates to a coke plant includingmultiple coke ovens, wherein each coke oven is adapted to produce cokeand exhaust gases, a common tunnel fluidly connected to the coke ovensand configured to receive the exhaust gases from each of the coke ovens,multiple standard heat recovery steam generators fluidly connected tothe common tunnel, a redundant heat recovery steam generator fluidlyconnected to the common tunnel wherein any one of the standard heatrecovery steam generators and the redundant heat recovery steamgenerator is adapted to receive the exhaust gases from the plurality ofovens and extract heat from the exhaust gases and wherein the standardheat recovery steam generators and the redundant heat recovery steamgenerator are all fluidly connected in parallel with each other, andmultiple crossover ducts, wherein each of the heat recovery steamgenerators and the redundant heat recovery steam generator is connectedto the common tunnel by one of the plurality of crossover ducts andwherein the ratio of ovens to crossover ducts is at least 50:3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a horizontal heat recovery (HHR) cokeplant, shown according to an exemplary embodiment.

FIG. 2 is a perspective view of portion of the HHR coke plant of FIG. 1,with several sections cut away.

FIG. 3 is a schematic drawing of a HHR coke plant, shown according to anexemplary embodiment.

FIG. 4 is a schematic drawing of a HHR coke plant, shown according to anexemplary embodiment.

FIG. 5 is a schematic drawing of a HHR coke plant, shown according to anexemplary embodiment.

FIG. 6 is a schematic drawing of a HHR coke plant, shown according to anexemplary embodiment.

FIG. 7 is a schematic view of a portion of the coke plant of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a HHR coke plant 100 is illustrated which producescoke from coal in a reducing environment. In general, the HHR coke plant100 comprises at least one oven 105, along with heat recovery steamgenerators (HRSGs) 120 and an air quality control system 130 (e.g. anexhaust or flue gas desulfurization (FGD) system) both of which arepositioned fluidly downstream from the ovens and both of which arefluidly connected to the ovens by suitable ducts. The HHR coke plant 100preferably includes a plurality of ovens 105 and a common tunnel 110fluidly connecting each of the ovens 105 to a plurality of HRSGs 120.One or more crossover ducts 115 fluidly connects the common tunnel 110to the HRSGs 120. A cooled gas duct 125 transports the cooled gas fromthe HRSG to the flue gas desulfurization (FGD) system 130. Fluidlyconnected and further downstream are a baghouse 135 for collectingparticulates, at least one draft fan 140 for controlling air pressurewithin the system, and a main gas stack 145 for exhausting cooled,treated exhaust to the environment. Steam lines 150 interconnect theHRSG and a cogeneration plant 155 so that the recovered heat can beutilized. As illustrated in FIG. 1, each “oven” shown represents tenactual ovens.

More structural detail of each oven 105 is shown in FIG. 2 whereinvarious portions of four coke ovens 105 are illustrated with sectionscut away for clarity. Each oven 105 comprises an open cavity preferablydefined by a floor 160, a front door 165 forming substantially theentirety of one side of the oven, a rear door 170 preferably oppositethe front door 165 forming substantially the entirety of the side of theoven opposite the front door, two sidewalls 175 extending upwardly fromthe floor 160 intermediate the front 165 and rear 170 doors, and a crown180 which forms the top surface of the open cavity of an oven chamber185. Controlling air flow and pressure inside the oven chamber 185 canbe critical to the efficient operation of the coking cycle and thereforethe front door 165 includes one or more primary air inlets 190 thatallow primary combustion air into the oven chamber 185. Each primary airinlet 190 includes a primary air damper 195 which can be positioned atany of a number of positions between fully open and fully closed to varythe amount of primary air flow into the oven chamber 185. Alternatively,the one or more primary air inlets 190 are formed through the crown 180.In operation, volatile gases emitted from the coal positioned inside theoven chamber 185 collect in the crown and are drawn downstream in theoverall system into downcomer channels 200 formed in one or bothsidewalls 175. The downcomer channels fluidly connect the oven chamber185 with a sole flue 205 positioned beneath the over floor 160. The soleflue 205 forms a circuitous path beneath the oven floor 160. Volatilegases emitted from the coal can be combusted in the sole flue 205thereby generating heat to support the reduction of coal into coke. Thedowncomer channels 200 are fluidly connected to uptake channels 210formed in one or both sidewalls 175. A secondary air inlet 215 isprovided between the sole flue 205 and atmosphere and the secondary airinlet 215 includes a secondary air damper 220 that can be positioned atany of a number of positions between fully open and fully closed to varythe amount of secondary air flow into the sole flue 205. The uptakechannels 210 are fluidly connected to the common tunnel 110 by one ormore uptake ducts 225. A tertiary air inlet 227 is provided between theuptake duct 225 and atmosphere. The tertiary air inlet 227 includes atertiary air damper 229 which can be positioned at any of a number ofpositions between fully open and fully closed to vary the amount oftertiary air flow into the uptake duct 225.

In order to provide the ability to control gas flow through the uptakeducts 225 and within ovens 105, each uptake duct 225 also includes anuptake damper 230. The uptake damper 230 can be positioned at number ofpositions between fully open and fully closed to vary the amount of ovendraft in the oven 105. As used herein, “draft” indicates a negativepressure relative to atmosphere. For example a draft of 0.1 inches ofwater indicates a pressure 0.1 inches of water below atmosphericpressure. Inches of water is a non-SI unit for pressure and isconventionally used to describe the draft at various locations in a cokeplant. If a draft is increased or otherwise made larger, the pressuremoves further below atmospheric pressure. If a draft is decreased,drops, or is otherwise made smaller or lower, the pressure moves towardsatmospheric pressure. By controlling the oven draft with the uptakedamper 230, the air flow into the oven from the air inlets 190, 215, 227as well as air leaks into the oven 105 can be controlled. Typically, anoven 105 includes two uptake ducts 225 and two uptake dampers 230, butthe use of two uptake ducts and two uptake dampers is not a necessity, asystem can be designed to use just one or more than two uptake ducts andtwo uptake dampers.

In operation, coke is produced in the ovens 105 by first loading coalinto the oven chamber 185, heating the coal in an oxygen depletedenvironment, driving off the volatile fraction of coal and thenoxidizing the volatiles within the oven 105 to capture and utilize theheat given off. The coal volatiles are oxidized within the ovens over a48-hour coking cycle, and release heat to regeneratively drive thecarbonization of the coal to coke. The coking cycle begins when thefront door 165 is opened and coal is charged onto the oven floor 160.The coal on the oven floor 160 is known as the coal bed. Heat from theoven (due to the previous coking cycle) starts the carbonization cycle.Preferably, no additional fuel other than that produced by the cokingprocess is used. Roughly half of the total heat transfer to the coal bedis radiated down onto the top surface of the coal bed from the luminousflame and radiant oven crown 180. The remaining half of the heat istransferred to the coal bed by conduction from the oven floor 160 whichis convectively heated from the volatilization of gases in the sole flue205. In this way, a carbonization process “wave” of plastic flow of thecoal particles and formation of high strength cohesive coke proceedsfrom both the top and bottom boundaries of the coal bed at the samerate, preferably meeting at the center of the coal bed after about 45-48hours.

Accurately controlling the system pressure, oven pressure, flow of airinto the ovens, flow of air into the system, and flow of gases withinthe system is important for a wide range of reasons including to ensurethat the coal is fully coked, effectively extract all heat of combustionfrom the volatile gases, effectively controlling the level of oxygenwithin the oven chamber 185 and elsewhere in the coke plant 100,controlling the particulates and other potential pollutants, andconverting the latent heat in the exhaust gases to steam which can beharnessed for generation of steam and/or electricity. Preferably, eachoven 105 is operated at negative pressure so air is drawn into the ovenduring the reduction process due to the pressure differential betweenthe oven 105 and atmosphere. Primary air for combustion is added to theoven chamber 185 to partially oxidize the coal volatiles, but the amountof this primary air is preferably controlled so that only a portion ofthe volatiles released from the coal are combusted in the oven chamber185 thereby releasing only a fraction of their enthalpy of combustionwithin the oven chamber 185. The primary air is introduced into the ovenchamber 185 above the coal bed through the primary air inlets 190 withthe amount of primary air controlled by the primary air dampers 195. Theprimary air dampers 195 can be used to maintain the desired operatingtemperature inside the oven chamber 185. The partially combusted gasespass from the oven chamber 185 through the downcomer channels 200 intothe sole flue 205 where secondary air is added to the partiallycombusted gases. The secondary air is introduced through the secondaryair inlet 215 with the amount of secondary air controlled by thesecondary air damper 220. As the secondary air is introduced, thepartially combusted gases are more fully combusted in the sole flue 205extracting the remaining enthalpy of combustion which is conveyedthrough the oven floor 160 to add heat to the oven chamber 185. Thenearly fully combusted exhaust gases exit the sole flue 205 through theuptake channels 210 and then flow into the uptake duct 225. Tertiary airis added to the exhaust gases via the tertiary air inlet 227 with theamount of tertiary air controlled by the tertiary air damper 229 so thatany remaining fraction of uncombusted gases in the exhaust gases areoxidized downstream of the tertiary air inlet 227.

At the end of the coking cycle, the coal has carbonized to produce coke.The coke is preferably removed from the oven 105 through the rear door170 utilizing a mechanical extraction system. Finally, the coke isquenched (e.g., wet or dry quenched) and sized before delivery to auser.

As shown in FIG. 1, a sample HHR coke plant 100 includes a number ofovens 105 that are grouped into oven blocks 235. The illustrated HHRcoke plant 100 includes five oven blocks 235 of twenty ovens each, for atotal of one hundred ovens. All of the ovens 105 are fluidly connectedby at least one uptake duct 225 to the common tunnel 110 which is inturn fluidly connected to each HRSG 120 by a crossover duct 115. Eachoven block 235 is associated with a particular crossover duct 115. Undernormal operating conditions, the exhaust gases from each oven 105 in anoven block 235 flow through the common tunnel 110 to the crossover duct115 associated with each respective oven block 235. Half of the ovens inan oven block 235 are located on one side of an intersection 245 of thecommon tunnel 110 and a crossover duct 115 and the other half of theovens in the oven block 235 are located on the other side of theintersection 245. Under normal operating conditions there will be littleor no net flow along the length of the common tunnel 110; instead, theexhaust gases from each oven block 235 will typically flow through thecrossover duct 115 associated with that oven block 235 to the relatedHRSG 120.

In the HRSG 120, the latent heat from the exhaust gases expelled fromthe ovens 105 is recaptured and preferably used to generate steam. Thesteam produced in the HRSGs 120 is routed via steam lines 150 to thecogeneration plant 155, where the steam is used to generate electricity.After the latent heat from the exhaust gases has been extracted andcollected, the cooled exhaust gases exit the HRSG 120 and enter thecooled gas duct 125. All of the HRSGs 120 are fluidly connected to thecooled gas duct 125. With this structure, all of the components betweenthe ovens 105 and the cooled gas duct 125 including the uptake ducts225, the common tunnel 110, the crossover duct 115 s, and the HRSGs 120form the hot exhaust system. The combined cooled exhaust gases from allof the HRSGs 120 flow to the FGD system 130, where sulfur oxides(SO_(X)) are removed from the cooled exhaust gases. The cooled,desulfurized exhaust gases flow from the FGD system 130 to the baghouse135, where particulates are removed, resulting in cleaned exhaust gases.The cleaned exhaust gases exit the baghouse 135 through the draft fan140 and are dispersed to the atmosphere via the main gas stack 145. Thedraft fan 140 creates the draft required to cause the described flow ofexhaust gases and depending upon the size and operation of the system,one or more draft fans 140 can be used. Preferably, the draft fan 140 isan induced draft fan. The draft fan 140 can be controlled to vary thedraft through the coke plant 100. Alternatively, no draft fan 140 isincluded and the necessary draft is produced due to the size of the maingas stack 145.

Under normal operating conditions, the entire system upstream of thedraft fan 140 is maintained at a draft. Therefore, during operation,there is a slight bias of airflow from the ovens 105 through the entiresystem to the draft fan 140. For emergency situations, a bypass exhauststack 240 is provided for each oven block 235. Each bypass exhaust stack240 is located at an intersection 245 between the common tunnel 110 anda crossover duct 115. Under emergency situations, hot exhaust gasesemanating from the oven block 235 associated with a crossover duct 115can be vented to atmosphere via the related bypass exhaust stack 240.The release of hot exhaust gas through the bypass exhaust stack 240 isundesirable for many reasons including environmental concerns and energyconsumption. Additionally, the output of the cogeneration plant 155 isreduced because the offline HRSG 120 is not producing steam.

In a conventional HHR coke plant when a HRSG is offline due to scheduledmaintenance, an unexpected emergency, or other reason, the exhaust gasesfrom the associated oven block can be vented to atmosphere through theassociated bypass exhaust stack because there is nowhere else for theexhaust gases to go due to gas flow limitations imposed by the commontunnel design and draft. If the exhaust gases were not vented toatmosphere through the bypass exhaust stack, they would cause undesiredoutcomes (e.g., positive pressure relative to atmosphere in an oven orovens, damage to the offline HRSG) at other locations in the coke plant.

In the HHR coke plant 100 described herein, it is possible to avoid theundesirable loss of untreated exhaust gases to the environment bydirecting the hot exhaust gases that would normally flow to an offlineHRSG to one or more of the online HRSGs 120. In other words, it ispossible to share the exhaust or flue gases of each oven block 235 alongthe common tunnel 110 and among multiple HRSGs 120 rather than aconventional coke plant where the vast majority of exhaust gases from anoven block flow to the single HRSG associated with that oven block.While some amount of exhaust gases may flow along the common tunnel of aconventional coke plant (e.g., from a first oven block to the HRSGassociated with the adjacent oven block), a conventional coke plantcannot be operated to transfer all of the exhaust gases from an ovenblock associated with an offline HRSG to one or more online HRSGs. Inother words, it is not possible in a conventional coke plant for all ofthe exhaust gases that would typically flow to a first offline HRSG tobe transferred or gas shared along the common tunnel to one or moredifferent online HRSGs. “Gas sharing” is possible by implementing anincreased effective flow area of the common tunnel 110, an increaseddraft in the common tunnel 110, the addition of at least one redundantHRSG 120R, as compared to a conventional HHR coke plant, and byconnecting all of the HRSGs 120 (standard and redundant) in parallelwith each other. With gas sharing, it is possible to eliminate theundesirable expulsion of hot gases through the bypass exhaust stacks240. In an example of a conventional HHR coke plant, an oven block oftwenty coke ovens and a single HRSG are fluidly connected via a firstcommon tunnel, two oven blocks totaling forty coke ovens and two HRSGsare connected by a second common tunnel, and two oven blocks totalingforty coke ovens and two HRSGs are connected by a third common tunnel,but gas sharing of all of the exhaust gases along the second commontunnel and along the third common tunnel from an oven block associatedwith an offline HRSG to the remaining online HRSG is not possible.

Maintaining drafts having certain minimum levels or targets with the hotexhaust gas sharing system is necessary for effective gas sharingwithout adversely impacting the performance of the ovens 105. The valuesrecited for various draft targets are measured under normal steady-stateoperating conditions and do not include momentary, intermittent, ortransient fluctuations in the draft at the specified location. Each oven105 must maintain a draft (“oven draft”), that is, a negative pressurerelative to atmosphere. Typically, the targeted oven draft is at least0.1 inches of water. In some embodiments, the oven draft is measured inthe oven chamber 185. During gas sharing along the common tunnel 110,the “intersection draft” at one or more of the intersections 245 betweenthe common tunnel 110 and the crossover ducts 115 and/or the “commontunnel draft” at one or more locations along the common tunnel 110 mustbe above a targeted draft (e.g., at least 0.7 inches of water) to ensureproper operation of the system. The common tunnel draft is measuredupstream of the intersection draft (i.e., between an intersection 245and the coke ovens 105) and is therefore typically lower than theintersection draft. In some embodiments the targeted intersection draftand/or the targeted common tunnel draft during gas sharing can be atleast 1.0 inches of water and in other embodiments the targetedintersection draft and/or the targeted common tunnel draft during gassharing can be at least 2.0 inches of water. Hot exhaust gas sharingeliminates the discharge of hot exhaust gases to atmosphere andincreases the efficiency of the cogeneration plant 155. It is importantto note that a hot exhaust gas sharing HHR coke plant 100 as describedherein can be newly constructed or an existing, conventional HHR cokeplant can be retrofitted according to the innovations described herein.

In an exhaust gas sharing system in which one or more HRSG 120 isoffline, the hot exhaust gases ordinarily sent to the offline HRSGs 120are not vented to atmosphere through the related bypass exhaust stack240, but are instead routed through the common tunnel 110 to one or moredifferent HRSGs 120. To accommodate the increased volume of gas flowthrough the common tunnel 110 during gas sharing, the effective flowarea of the common tunnel 110 is greater than that of the common tunnelin a conventional HHR coke plant. This increased effective flow area canbe achieved by increasing the inner diameter of the common tunnel 110 orby adding one or more additional common tunnels 110 to the hot exhaustsystem in parallel with the existing common tunnel 110 (as shown in FIG.3). In one embodiment, the single common tunnel 110 has an effectiveflow inner diameter of nine feet. In another embodiment, the singlecommon tunnel 110 has an effective flow inner diameter of eleven feet.Alternatively, a dual common tunnel configuration, a multiple commontunnel configuration, or a hybrid dual/multiple tunnel configuration canbe used. In a dual common tunnel configuration, the hot exhaust gassesfrom all of the ovens are directly distributed to two parallel, oralmost parallel, common tunnels, which can be fluidly connected to eachother at different points along the tunnels' length. In a multiplecommon tunnel configuration, the hot exhaust gasses from all of theovens are directly distributed to two or more parallel, or almostparallel common hot tunnels, which can be fluidly connected to eachother at different points along the tunnels' length. In a hybriddual/multiple common tunnel, the hot exhaust gasses from all of theovens are directly distributed to two or more parallel, or almostparallel, hot tunnels, which can be fluidly connected to each other atdifferent points along the tunnels' length. However, one, two, or moreof the hot tunnels may not be a true common tunnel. For example, one orboth of the hot tunnels may have partitions or be separated along thelength of its run.

Hot exhaust gas sharing also requires that during gas sharing the commontunnel 110 be maintained at a higher draft than the common tunnel of aconventional HHR coke plant. In a conventional HHR coke plant, theintersection draft and the common tunnel draft are below 0.7 inches ofwater under normal steady-state operating conditions. A conventional HHRcoke plant has never been operated such that the common tunnel operatesat a high intersection draft or a high common tunnel draft (at or above0.7 inches of water) because of concerns that the high intersectiondraft and the high common tunnel draft would result in excess air in theoven chambers. To allow for gas sharing along the common tunnel 110, theintersection draft at one or more intersections 245 must be maintainedat least at 0.7 inches of water. In some embodiments, the intersectiondraft at one or more intersections 245 is maintained at least at 1.0inches of water or at least at 2.0 inches of water. Alternatively oradditionally, to allow for gas sharing along the common tunnel 110, thecommon tunnel draft at one or more locations along the common tunnel 110must be maintained at least at 0.7 inches of water. In some embodiments,the common tunnel draft at one or more locations along the common tunnel110 is maintained at least at 1.0 inches of water or at least at 2.0inches of water. Maintaining such a high draft at one or moreintersections 245 or at one or more locations along the common tunnel110 ensures that the oven draft in all of the ovens 105 will be at least0.1 inches of water when a single HSRG 120 is offline and providessufficient draft for the exhaust gases from the oven block 235associated with the offline HRSG 120 to flow to an online HSRG 120.While in the gas sharing operating mode (i.e., when at least one HRSG120 is offline), the draft along the common tunnel 110 and at thedifferent intersections 245 will vary. For example, if the HRSG 120closest to one end of the common tunnel 110 is offline, the commontunnel draft at the proximal end of the common tunnel 110 will be around0.1 inches of water and the common tunnel draft at the opposite, distalend of the common tunnel 110 will be around 1.0 inches of water.Similarly, the intersection draft at the intersection 245 furthest fromthe offline HRSG 120 will be relatively high (i.e., at least 0.7 inchesof water) and the intersection draft at the intersection 245 associatedwith the offline HRSG 120 will be relatively low (i.e., lower than theintersection draft at the previously-mentioned intersection 245 andtypically below 0.7 inches of water).

Alternatively, the HHR coke plant 100 can be operated in two operatingmodes: a normal operating mode for when all of the HRSGs 120 are onlineand a gas sharing operating mode for when at least one of the HRSGs 120is offline. In the normal operating mode, the common tunnel 110 ismaintained at a common tunnel draft and intersection drafts similar tothose of a conventional HHR coke plant (typically, the intersectiondraft is between 0.5 and 0.6 inches of water and the common tunnel draftat a location near the intersection is between 0.4 and 0.5 inches ofwater). The common tunnel draft and the intersection draft can varyduring the normal operating mode and during the gas sharing mode. Inmost situations, when a HRSG 120 goes offline, the gas sharing modebegins and the intersection draft at one or more intersections 245and/or the common tunnel draft at one or more locations along the commontunnel 110 is raised. In some situations, for example, when the HRSG 120furthest from the redundant HRSG 120R is offline, the gas sharing modewill begin and will require an intersection draft and/or a common tunneldraft of at least 0.7 inches of water (in some embodiments, between 1.2and 1.3 inches of water) to allow for gas sharing along the commontunnel 110. In other situations, for example, when a HRSG 120 positionednext to the redundant HRSG 120R which is offline, the gas sharing modemay not be necessary, that is gas sharing may be possible in the normaloperating mode with the same operating conditions prior to the HRSG 120going offline, or the gas sharing mode will begin and will require onlya slight increase in the intersection draft and/or a common tunneldraft. In general, the need to go to a higher draft in the gas sharingmode will depend on where the redundant HRSG 120R is located relative tothe offline HRSG 120. The further away the redundant HRSG 120R fluidlyis form the tripped HRSG 120, the higher the likelihood that a higherdraft will be needed in the gas sharing mode.

Increasing the effective flow area and the intersection draft and/or thecommon tunnel draft to the levels described above also allows for moreovens 105 to be added to an oven block 235. In some embodiments, up toone hundred ovens form an oven block (i.e., are associated with acrossover duct).

The HRSGs 120 found in a conventional HHR coke plant at a ratio oftwenty ovens to one HRSG are referred to as the “standard HRSGs.” Theaddition of one or more redundant HRSGs 120R results in an overall ovento HRSG ratio of less than 20:1. Under normal operating conditions, thestandard HRSGs 120 and the redundant HRSG 120R are all in operation. Itis impractical to bring the redundant HRSG 120R online and offline asneeded because the start-up time for a HRSG would result in theredundant HRSG 120R only being available on a scheduled basis and notfor emergency purposes. An alternative to installing one or moreredundant HRSGs would be to increase the capacity of the standard HRSGsto accommodate the increased exhaust gas flow during gas sharing. Undernormal operating conditions with all of the high capacity HRSGs online,the exhaust gases from each oven block are conveyed to the associatedhigh capacity HRSGs. In the event that one of the high capacity HRSGsgoes offline, the other high capacity HRSGs would be able to accommodatethe increased flow of exhaust gases.

In a gas sharing system as described herein, when one of the HRSGs 120is offline the exhaust gases emanating from the various ovens 105 areshared and distributed among the remaining online HRSGs 120 such that aportion of the total exhaust gases are routed through the common tunnel110 to each of the online HRSGs 120 and no exhaust gas is vented toatmosphere. The exhaust gases are routed amongst the various HRSGs 120by adjusting a HRSG valve 250 associated with each HRSG 120 (shown inFIG. 1). The HRSG valve 250 can be positioned on the upstream or hotside of the HRSG 120, but is preferably positioned on the downstream orcold side of the HRSG 120. The HRSG valves 250 are variable to a numberof positions between fully opened and fully closed and the flow ofexhaust gases through the HRSGs 120 is controlled by adjusting therelative position of the HRSG valves 250. When gas is shared, some orall of the operating HRSGs 120 will receive additional loads. Because ofthe resulting different flow distributions when a HRSG 120 is offline,the common tunnel draft along the common tunnel 110 will change. Thecommon tunnel 110 helps to better distribute the flow among the HRSGs120 to minimize the pressure differences throughout the common tunnel110. The common tunnel 110 is sized to help minimize peak flowvelocities (e.g. below 120 ft/s) and to reduce potential erosion andacoustic concerns (e.g. noise levels below 85 dB at 3 ft). When an HRSG120 is offline, there can be higher than normal peak mass flow rates inthe common tunnel, depending on which HRSG 120 is offline. During suchgas sharing periods, the common tunnel draft may need to be increased tomaintain the targeted oven drafts, intersection drafts, and commontunnel draft.

In general, a larger common tunnel 110 can correlate to larger allowablemass flow rates relative to a conventional common tunnel for the samegiven desired pressure difference along the length of the common tunnel110. The converse is also true, the larger common tunnel 110 cancorrelate to smaller pressure differences relative to a conventionalcommon tunnel for the same given desired mass flow rate along the lengthof the common tunnel 110. Larger means larger effective flow area andnot necessarily larger geometric cross sectional area. Higher commontunnel drafts can accommodate larger mass flow rates through the commontunnel 110. In general, higher temperatures can correlate to lowerallowable mass flow rates for the same given desired pressure differencealong the length of the tunnel. Higher exhaust gas temperatures shouldresult in volumetric expansion of the gases. Since the total pressurelosses can be approximately proportional to density and proportional tothe square of the velocity, the total pressure losses can be higher forvolumetric expansion because of higher temperatures. For example, anincrease in temperature can result in a proportional decrease indensity. However, an increase in temperature can result in anaccompanying proportional increase in velocity which affects the totalpressure losses more severely than the decrease in density. Since theeffect of velocity on total pressure can be more of a squared effectwhile the density effect can be more of a linear one, there should belosses in total pressure associated with an increase in temperature forthe flow in the common tunnel 110. Multiple, parallel, fluidly connectedcommon tunnels (dual, multiple, or hybrid dual/multiple configurations)may be preferred for retrofitting existing conventional HHR coke plantsinto the gas sharing HHR coke plants described herein.

Although the sample gas-sharing HHR coke plant 100 illustrated in FIG. 1includes one hundred ovens and six HRSGs (five standard HRSGs and oneredundant HRSG), other configurations of gas-sharing HHR coke plants 100are possible. For example, a gas-sharing HHR coke plant similar to theone illustrated in FIG. 1 could include one hundred ovens, and sevenHRSGs (five standard HRSGs sized to handle the exhaust gases from up totwenty ovens and two redundant HRSGs sized to handle the exhaust gasesfrom up to ten ovens (i.e., smaller capacity than the single redundantHRSG used in the coke plant 100 illustrated in FIG. 1)).

As shown in FIG. 3, in HHR coke plant 255, an existing conventional HHRcoke plant has been retrofitted to a gas-sharing coke plant. Existingpartial common tunnels 110A, 110B, and 110C each connect a bank of fortyovens 105. An additional common tunnel 260 fluidly connected to all ofthe ovens 105 has been added to the existing partial common tunnels110A, 110B, and 110C. The additional common tunnel 260 is connected toeach of the crossover ducts 115 extending between the existing partialcommon tunnels 110A, 110B, and 110C and the standard HRSGs 120. Theredundant HRSG 120R is connected to the additional common tunnel 260 bya crossover duct 265 extending to the additional common tunnel 260. Toallow for gas sharing, the intersection draft at one or moreintersections 245 between the existing partial common tunnels 110A,110B, 110C and the crossover ducts 115 and/or the common tunnel draft atone or more location along each of the partial common tunnels 110A,110B, 110C must be maintained at least at 0.7 inches of water. The draftat one or more of the intersections 270 between the additional commontunnel 260 and the crossover ducts 115 and 265 will be higher than 0.7inches of water (e.g., 1.5 inches of water). In some embodiments, theinner effective flow diameter of the additional common tunnel 260 can beas small as eight feet or as large as eleven feet. In one embodiment,the inner effective flow diameter of the additional common tunnel 260 isnine feet. Alternatively, as a further retrofit, the partial commontunnels 110A, 110B, and 110C are fluidly connected to one another,effectively creating two common tunnels (i.e., the combination of commontunnels 110A, 110B, and 110C and the additional common tunnel 260).

As shown in FIG. 4, in HHR coke plant 275, a single crossover duct 115fluidly connects three high capacity HRSGs 120 to two partial commontunnels 110A and 110B. The single crossover duct 115 essentiallyfunctions as a header for the HRSGs 120. The first partial common tunnel110A services an oven block of sixty ovens 105 with thirty ovens 105 onone side of the intersection 245 between the partial common tunnel 110Aand the crossover duct 115 and thirty ovens 105 on the opposite side ofthe intersection 245. The ovens 105 serviced by the second partialcommon tunnel 110B are similarly arranged. The three high capacity HRSGsare sized so that only two HRSGs are needed to handle the exhaust gasesfrom all one hundred twenty ovens 105, enabling one HRSG to be takenoffline without having to vent exhaust gases through a bypass exhauststack 240. The HHR coke plant 275 can be viewed as having one hundredtwenty ovens and three HRSGs (two standard HRSGs and one redundant HRSG)for an oven to standard HRSG ratio of 60:1. Alternatively, as shown inFIG. 5, in the HHR coke plant 280, a redundant HRSG 120R is added to sixstandard HRSGs 120 instead of using the three high capacity HRSGs 120shown in FIG. 4. The HHR coke plant 280 can be viewed as having onehundred twenty ovens and seven HRSGs (six standard HRSGs and oneredundant HRSG) for an oven to standard HRSG ratio of 20:1). In someembodiments, coke plants 275 and 280 are operated at least duringperiods of maximum mass flow rates through the intersections 245 tomaintain a target intersection draft at one or more of the intersections245 and/or a target common tunnel draft at one or more locations alongeach of the common tunnels 110A and 110B of at least 0.7 inches ofwater. In one embodiment, the target intersection draft at one or moreof the intersections 245 and/or the target common tunnel draft at one ormore locations along each of the common tunnels 110A and 110B is 0.8inches of water. In another embodiment, the target intersection draft atone or more of the intersections 245 and/or the common tunnel draft atone or more locations along each of the common tunnels 110A and 110B is1.0 inches of water. In other embodiments, the target intersection draftat one or more of the intersections 245 and/or the target common tunneldraft at one or more locations along each of the common tunnels 110A and110B is greater than 1.0 inches of water and can be 2.0 inches of wateror higher.

As shown in FIG. 6, in HHR coke plant 285, a first crossover duct 290connects a first partial common tunnel 110A to three high capacity HRSGs120 arranged in parallel and a second crossover duct 295 connects asecond partial common tunnel 110B to the three high capacity HRSGs 120.The first partial common tunnel 110A services an oven block of sixtyovens 105 with thirty ovens 105 on one side of the intersection 245between the first partial common tunnel 110A and the first crossoverduct 290 and thirty ovens 105 on the opposite side of the intersection245. The second partial common tunnel 110B services an oven block ofsixty ovens 105 with thirty ovens 105 on one side of the intersection245 between the second common tunnel 110B and the second crossover duct295 and thirty ovens 105 on the opposite side of the intersection 245.The three high capacity HRSGs are sized so that only two HRSGs areneeded to handle the exhaust gases from all one hundred twenty ovens105, enabling one HRSG to be taken offline without having to ventexhaust gases through a bypass exhaust stack 240. The HHR coke plant 285can be viewed as having one hundred twenty ovens and three HRSGs (twostandard HRSGs and one redundant HRSG) for an oven to standard HRSGratio of 60:1 In some embodiments, coke plant 285 is operated at leastduring periods of maximum mass flow rates through the intersections 245to maintain a target intersection draft at one or more of theintersections 245 and/or a target common tunnel draft at one or morelocations along each of the common tunnels 110A and 110B of at least 0.7inches of water. In one embodiment, the target intersection draft at oneor more of the intersections 245 and/or the target common tunnel draftat one or more locations along each of the common tunnels 110A and 110Bis 0.8 inches of water. In another embodiment, the target intersectiondraft at one or more of the intersections 245 and/or the common tunneldraft at one or more locations along each of the common tunnels 110A and110B is 1.0 inches of water. In other embodiments, the targetintersection draft at one or more of the intersections 245 and/or thetarget common tunnel draft at one or more locations along each of thecommon tunnels 110A and 110B is greater than 1.0 inches of water and canbe 2.0 inches of water or higher.

FIG. 7 illustrates a portion of the coke plant 100 including anautomatic draft control system 300. The automatic draft control system300 includes an automatic uptake damper 305 that can be positioned atany one of a number of positions between fully open and fully closed tovary the amount of oven draft in the oven 105. The automatic uptakedamper 305 is controlled in response to operating conditions (e.g.,pressure or draft, temperature, oxygen concentration, gas flow rate)detected by at least one sensor. The automatic control system 300 caninclude one or more of the sensors discussed below or other sensorsconfigured to detect operating conditions relevant to the operation ofthe coke plant 100.

An oven draft sensor or oven pressure sensor 310 detects a pressure thatis indicative of the oven draft and the oven draft sensor 310 can belocated in the oven crown 180 or elsewhere in the oven chamber 185.Alternatively, the oven draft sensor 310 can be located at either of theautomatic uptake dampers 305, in the sole flue 205, at either oven door165 or 170, or in the common tunnel 110 near above the coke oven 105. Inone embodiment, the oven draft sensor 310 is located in the top of theoven crown 180. The oven draft sensor 310 can be located flush with therefractory brick lining of the oven crown 180 or could extend into theoven chamber 185 from the oven crown 180. A bypass exhaust stack draftsensor 315 detects a pressure that is indicative of the draft at thebypass exhaust stack 240 (e.g., at the base of the bypass exhaust stack240). In some embodiments, the bypass exhaust stack draft sensor 315 islocated at the intersection 245. Additional draft sensors can bepositioned at other locations in the coke plant 100. For example, adraft sensor in the common tunnel could be used to detect a commontunnel draft indicative of the oven draft in multiple ovens proximatethe draft sensor. An intersection draft sensor 317 detects a pressurethat is indicative of the draft at one of the intersections 245.

An oven temperature sensor 320 detects the oven temperature and can belocated in the oven crown 180 or elsewhere in the oven chamber 185. Asole flue temperature sensor 325 detects the sole flue temperature andis located in the sole flue 205. In some embodiments, the sole flue 205is divided into two labyrinths 205A and 205B with each labyrinth influid communication with one of the oven's two uptake ducts 225. A fluetemperature sensor 325 is located in each of the sole flue labyrinths sothat the sole flue temperature can be detected in each labyrinth. Anuptake duct temperature sensor 330 detects the uptake duct temperatureand is located in the uptake duct 225. A common tunnel temperaturesensor 335 detects the common tunnel temperature and is located in thecommon tunnel 110. A HRSG inlet temperature sensor 340 detects the HRSGinlet temperature and is located at or near the inlet of the HRSG 120.Additional temperature sensors can be positioned at other locations inthe coke plant 100.

An uptake duct oxygen sensor 345 is positioned to detect the oxygenconcentration of the exhaust gases in the uptake duct 225. An HRSG inletoxygen sensor 350 is positioned to detect the oxygen concentration ofthe exhaust gases at the inlet of the HRSG 120. A main stack oxygensensor 360 is positioned to detect the oxygen concentration of theexhaust gases in the main stack 145 and additional oxygen sensors can bepositioned at other locations in the coke plant 100 to provideinformation on the relative oxygen concentration at various locations inthe system.

A flow sensor detects the gas flow rate of the exhaust gases. Forexample, a flow sensor can be located downstream of each of the HRSGs120 to detect the flow rate of the exhaust gases exiting each HRSG 120.This information can be used to balance the flow of exhaust gasesthrough each HRSG 120 by adjusting the HRSG dampers 250 and therebyoptimize gas sharing among the HRSGs 120. Additional flow sensors can bepositioned at other location sin the coke plant 100 to provideinformation on the gas flow rate at various locations in the system.

Additionally, one or more draft or pressure sensors, temperaturesensors, oxygen sensors, flow sensors, and/or other sensors may be usedat the air quality control system 130 or other locations downstream ofthe HRSGs 120.

It can be important to keep the sensors clean. One method of keeping asensor clean is to periodically remove the sensor and manually clean it.Alternatively, the sensor can be periodically subjected to a burst,blast, or flow of a high pressure gas to remove build up at the sensor.As a further alternatively, a small continuous gas flow can be providedto continually clean the sensor.

The automatic uptake damper 305 includes the uptake damper 230 and anactuator 365 configured to open and close the uptake damper 230. Forexample, the actuator 365 can be a linear actuator or a rotationalactuator. The actuator 365 allows the uptake damper 230 to be infinitelycontrolled between the fully open and the fully closed positions. Theactuator 365 moves the uptake damper 230 amongst these positions inresponse to the operating condition or operating conditions detected bythe sensor or sensors included in the automatic draft control system300. This provides much greater control than a conventional uptakedamper. A conventional uptake damper has a limited number of fixedpositions between fully open and fully closed and must be manuallyadjusted amongst these positions by an operator.

The uptake dampers 230 are periodically adjusted to maintain theappropriate oven draft (e.g., at least 0.1 inches of water) whichchanges in response to many different factors within the ovens or thehot exhaust system. When the common tunnel 110 has a relatively lowcommon tunnel draft (i.e., closer to atmospheric pressure than arelatively high draft), the uptake damper 230 can be opened to increasethe oven draft to ensure the oven draft remains at or above 0.1 inchesof water. When the common tunnel 110 has a relatively high common tunneldraft, the uptake damper 230 can be closed to decrease the oven draft,thereby reducing the amount of air drawn into the oven chamber 185.

With conventional uptake dampers, the uptake dampers are manuallyadjusted and therefore optimizing the oven draft is part art and partscience, a product of operator experience and awareness. The automaticdraft control system 300 described herein automates control of theuptake dampers 230 and allows for continuous optimization of theposition of the uptake dampers 230 thereby replacing at least some ofthe necessary operator experience and awareness. The automatic draftcontrol system 300 can be used to maintain an oven draft at a targetedoven draft (e.g., at least 0.1 inches of water), control the amount ofexcess air in the oven 105, or achieve other desirable effects byautomatically adjusting the position of the uptake damper 230. Theautomatic draft control system 300 makes it easier to achieve the gassharing described above by allowing for a high intersection draft at oneor more of the intersections 245 and/or a high common tunnel draft atone or more locations along the common tunnel 110 while maintaining ovendrafts low enough to prevent excess air leaks into the ovens 105.Without automatic control, it would be difficult if not impossible tomanually adjust the uptake dampers 230 as frequently as would berequired to maintain the oven draft of at least 0.1 inches of waterwithout allowing the pressure in the oven to drift to positive.Typically, with manual control, the target oven draft is greater than0.1 inches of water, which leads to more air leakage into the coke oven105. For a conventional uptake damper, an operator monitors various oventemperatures and visually observes the coking process in the coke ovento determine when to and how much to adjust the uptake damper. Theoperator has no specific information about the draft (pressure) withinthe coke oven.

The actuator 365 positions the uptake damper 230 based on positioninstructions received from a controller 370. The position instructionscan be generated in response to the draft, temperature, oxygenconcentration, or gas flow rate detected by one or more of the sensorsdiscussed above, control algorithms that include one or more sensorinputs, or other control algorithms. The controller 370 can be adiscrete controller associated with a single automatic uptake damper 305or multiple automatic uptake dampers 305, a centralized controller(e.g., a distributed control system or a programmable logic controlsystem), or a combination of the two. In some embodiments, thecontroller 370 utilizes proportional-integral-derivative (“PID”)control.

The automatic draft control system 300 can, for example, control theautomatic uptake damper 305 of an oven 105 in response to the oven draftdetected by the oven draft sensor 310. The oven draft sensor 310 detectsthe oven draft and outputs a signal indicative of the oven draft to thecontroller 370. The controller 370 generates a position instruction inresponse to this sensor input and the actuator 365 moves the uptakedamper 230 to the position required by the position instruction. In thisway, the automatic control system 300 can be used to maintain a targetedoven draft (e.g., at least 0.1 inches of water). Similarly, theautomatic draft control system 300 can control the automatic uptakedampers 305, the HRSG dampers 250, and the draft fan 140, as needed, tomaintain targeted drafts at other locations within the coke plant 100(e.g., a targeted intersection draft or a targeted common tunnel draft).For example, for gas sharing as described above, the intersection draftat one or more intersections 245 and/or the common tunnel draft at oneor more locations along the common tunnel 110 needs to be maintained atleast at 0.7 inches of water. The automatic draft control system 300 canbe placed into a manual mode to allow for manual adjustment of theautomatic uptake dampers 305, the HRSG dampers, and/or the draft fan140, as needed. Preferably, the automatic draft control system 300includes a manual mode timer and upon expiration of the manual modetimer, the automatic draft control system 300 returns to automatic mode.

In some embodiments, the signal generated by the oven draft sensor 310that is indicative of the detected pressure or draft is time averaged toachieve a stable pressure control in the coke oven 105. The timeaveraging of the signal can be accomplished by the controller 370. Timeaveraging the pressure signal helps to filter out normal fluctuations inthe pressure signal and to filter out noise. Typically, the signal couldbe averaged over 30 seconds, 1 minute, 5 minutes, or over at least 10minutes. In one embodiment, a rolling time average of the pressuresignal is generated by taking 200 scans of the detected pressure at 50milliseconds per scan. The larger the difference in the time-averagedpressure signal and the target oven draft, the automatic draft controlsystem 300 enacts a larger change in the damper position to achieve thedesired target draft. In some embodiments, the position instructionsprovided by the controller 370 to the automatic uptake damper 305 arelinearly proportional to the difference in the time-averaged pressuresignal and the target oven draft. In other embodiments, the positioninstructions provided by the controller 370 to the automatic uptakedamper 305 are non-linearly proportional to the difference in thetime-averaged pressure signal and the target oven draft. The othersensors previously discussed can similarly have time-averaged signals.

The automatic draft control system 300 can be operated to maintain aconstant time-averaged oven draft within a specific tolerance of thetarget oven draft throughout the coking cycle. This tolerance can be,for example, +/−0.05 inches of water, +/−0.02 inches of water, or+/−0.01 inches of water.

The automatic draft control system 300 can also be operated to create avariable draft at the coke oven by adjusting the target oven draft overthe course of the coking cycle. The target oven draft can be stepwisereduced as a function of the elapsed time of the coking cycle. In thismanner, using a 48-hour coking cycle as an example, the target draftstarts out relatively high (e.g. 0.2 inches of water) and is reducedevery 12 hours by 0.05 inches of water so that the target oven draft is0.2 inches of water for hours 1-12 of the coking cycle, 0.15 inches ofwater for hours 12-24 of the coking cycle, 0.01 inches of water forhours 24-36 of the coking cycle, and 0.05 inches of water for hours36-48 of the coking cycle. Alternatively, the target draft can belinearly decreased throughout the coking cycle to a new, smaller valueproportional to the elapsed time of the coking cycle.

As an example, if the oven draft of an oven 105 drops below the targetedoven draft (e.g., 0.1 inches of water) and the uptake damper 230 isfully open, the automatic draft control system 300 would increase thedraft by opening at least one HRSG damper 250 to increase the ovendraft. Because this increase in draft downstream of the oven 105 affectsmore than one oven 105, some ovens 105 might need to have their uptakedampers 230 adjusted (e.g., moved towards the fully closed position) tomaintain the targeted oven draft (i.e., regulate the oven draft toprevent it from becoming too high). If the HRSG damper 250 was alreadyfully open, the automatic damper control system 300 would need to havethe draft fan 140 provide a larger draft. This increased draftdownstream of all the HRSGs 120 would affect all the HRSG 120 and mightrequire adjustment of the HRSG dampers 250 and the uptake dampers 230 tomaintain target drafts throughout the coke plant 100.

As another example, the common tunnel draft can be minimized byrequiring that at least one uptake damper 230 is fully open and that allthe ovens 105 are at least at the targeted oven draft (e.g. 0.1 inchesof water) with the HRSG dampers 250 and/or the draft fan 140 adjusted asneeded to maintain these operating requirements.

As another example, the coke plant 100 can be run at variable draft forthe intersection draft and/or the common tunnel draft to stabilize theair leakage rate, the mass flow, and the temperature and composition ofthe exhaust gases (e.g. oxygen levels), among other desirable benefits.This is accomplished by varying the intersection draft and/or the commontunnel draft from a relatively high draft (e.g. 0.8 inches of water)when the coke ovens 105 are pushed and reducing gradually to arelatively low draft (e.g. 0.4 inches of water), that is, running atrelatively high draft in the early part of the coking cycle and atrelatively low draft in the late part of the coking cycle. The draft canbe varied continuously or in a step-wise fashion.

As another example, if the common tunnel draft decreases too much, theHRSG damper 250 would open to raise the common tunnel draft to meet thetarget common tunnel draft at one or more locations along the commontunnel 110 (e.g., 0.7 inches water) to allow gas sharing. Afterincreasing the common tunnel draft by adjusting the HRSG damper 250, theuptake dampers 230 in the affected ovens 105 might be adjusted (e.g.,moved towards the fully closed position) to maintain the targeted ovendraft in the affected ovens 105 (i.e., regulate the oven draft toprevent it from becoming too high).

As another example, the automatic draft control system 300 can controlthe automatic uptake damper 305 of an oven 105 in response to the oventemperature detected by the oven temperature sensor 320 and/or the soleflue temperature detected by the sole flue temperature sensor or sensors325. Adjusting the automatic uptake damper 305 in response to the oventemperature and or the sole flue temperature can optimize cokeproduction or other desirable outcomes based on specified oventemperatures. When the sole flue 205 includes two labyrinths 205A and205B, the temperature balance between the two labyrinths 205A and 205Bcan be controlled by the automatic draft control system 300. Theautomatic uptake damper 305 for each of the oven's two uptake ducts 225is controlled in response to the sole flue temperature detected by thesole flue temperature sensor 325 located in labyrinth 205A or 205Bassociated with that uptake duct 225. The controller 370 compares thesole flue temperature detected in each of the labyrinths 205A and 205Band generates positional instructions for each of the two automaticuptake dampers 305 so that the sole flue temperature in each of thelabyrinths 205A and 205B remains within a specified temperature range.

In some embodiments, the two automatic uptake dampers 305 are movedtogether to the same positions or synchronized. The automatic uptakedamper 305 closest to the front door 165 is known as the “push-side”damper and the automatic uptake damper closet to the rear door 170 isknown as the “coke-side” damper. In this manner, a single oven draftpressure sensor 310 provides signals and is used to adjust both thepush- and coke-side automatic uptake dampers 305 identically. Forexample, if the position instruction from the controller to theautomatic uptake dampers 305 is at 60% open, both push- and coke-sideautomatic uptake dampers 305 are positioned at 60% open. If the positioninstruction from the controller to the automatic uptake dampers 305 is 8inches open, both push- and coke-side automatic uptake dampers 305 are 8inches open. Alternatively, the two automatic uptake dampers 305 aremoved to different positions to create a bias. For example, for a biasof 1 inch, if the position instruction for synchronized automatic uptakedampers 305 would be 8 inches open, for biased automatic uptake dampers305, one of the automatic uptake dampers 305 would be 9 inches open andthe other automatic uptake damper 305 would be 7 inches open. The totalopen area and pressure drop across the biased automatic uptake dampers305 remains constant when compared to the synchronized automatic uptakedampers 305. The automatic uptake dampers 305 can be operated insynchronized or biased manners as needed. The bias can be used to try tomaintain equal temperatures in the push-side and the coke-side of thecoke oven 105. For example, the sole flue temperatures measured in eachof the sole flue labyrinths 205A and 205B (one on the coke-side and theother on the push-side) can be measured and then corresponding automaticuptake damper 305 can be adjusted to achieve the target oven draft,while simultaneously using the difference in the coke- and push-sidesole flue temperatures to introduce a bias proportional to thedifference in sole flue temperatures between the coke-side sole flue andpush-side sole flue temperatures. In this way, the push- and coke-sidesole flue temperatures can be made to be equal within a certaintolerance. The tolerance (difference between coke- and push-side soleflue temperatures) can be 250° Fahrenheit, 100° Fahrenheit, 50°Fahrenheit, or, preferably 25° Fahrenheit or smaller. Usingstate-of-the-art control methodologies and techniques, the coke-sidesole flue and the push-side sole flue temperatures can be brought withinthe tolerance value of each other over the course of one or more hours(e.g. 1-3 hours), while simultaneously controlling the oven draft to thetarget oven draft within a specified tolerance (e.g. +/−0.01 inches ofwater). Biasing the automatic uptake dampers 305 based on the sole fluetemperatures measured in each of the sole flue labyrinths 205A and 205B,allows heat to be transferred between the push side and coke side of thecoke oven 105. Typically, because the push side and the coke side of thecoke bed coke at different rates, there is a need to move heat from thepush side to the coke side. Also, biasing the automatic uptake dampers305 based on the sole flue temperatures measured in each of the soleflue labyrinths 205A and 205B, helps to maintain the oven floor at arelatively even temperature across the entire floor.

The oven temperature sensor 320, the sole flue temperature sensor 325,the uptake duct temperature sensor 330, the common tunnel temperaturesensor 335, and the HRSG inlet temperature sensor 340 can be used todetect overheat conditions at each of their respective locations. Thesedetected temperatures can generate position instructions to allow excessair into one or more ovens 105 by opening one or more automatic uptakedampers 305. Excess air (i.e., where the oxygen present is above thestoichiometric ratio for combustion) results in uncombusted oxygen anduncombusted nitrogen in the oven 105 and in the exhaust gases. Thisexcess air has a lower temperature than the other exhaust gases andprovides a cooling effect that eliminates overheat conditions elsewherein the coke plant 100.

As another example, the automatic draft control system 300 can controlthe automatic uptake damper 305 of an oven 105 in response to uptakeduct oxygen concentration detected by the uptake duct oxygen sensor 345.Adjusting the automatic uptake damper 305 in response to the uptake ductoxygen concentration can be done to ensure that the exhaust gasesexiting the oven 105 are fully combusted and/or that the exhaust gasesexiting the oven 105 do not contain too much excess air or oxygen.Similarly, the automatic uptake damper 305 can be adjusted in responseto the HRSG inlet oxygen concentration detected by the HRSG inlet oxygensensor 350 to keep the HRSG inlet oxygen concentration above a thresholdconcentration that protects the HRSG 120 from unwanted combustion of theexhaust gases occurring at the HRSG 120. The HRSG inlet oxygen sensor350 detects a minimum oxygen concentration to ensure that all of thecombustibles have combusted before entering the HRSG 120. Also, theautomatic uptake damper 305 can be adjusted in response to the mainstack oxygen concentration detected by the main stack oxygen sensor 360to reduce the effect of air leaks into the coke plant 100. Such airleaks can be detected based on the oxygen concentration in the mainstack 145.

The automatic draft control system 300 can also control the automaticuptake dampers 305 based on elapsed time within the coking cycle. Thisallows for automatic control without having to install an oven draftsensor 310 or other sensor in each oven 105. For example, the positioninstructions for the automatic uptake dampers 305 could be based onhistorical actuator position data or damper position data from previouscoking cycles for one or more coke ovens 105 such that the automaticuptake damper 305 is controlled based on the historical positioning datain relation to the elapsed time in the current coking cycle.

The automatic draft control system 300 can also control the automaticuptake dampers 305 in response to sensor inputs from one or more of thesensors discussed above. Inferential control allows each coke oven 105to be controlled based on anticipated changes in the oven's or cokeplant's operating conditions (e.g., draft/pressure, temperature, oxygenconcentration at various locations in the oven 105 or the coke plant100) rather than reacting to the actual detected operating condition orconditions. For example, using inferential control, a change in thedetected oven draft that shows that the oven draft is dropping towardsthe targeted oven draft (e.g., at least 0.1 inches of water) based onmultiple readings from the oven draft sensor 310 over a period of time,can be used to anticipate a predicted oven draft below the targeted ovendraft to anticipate the actual oven draft dropping below the targetedoven draft and generate a position instruction based on the predictedoven draft to change the position of the automatic uptake damper 305 inresponse to the anticipated oven draft, rather than waiting for theactual oven draft to drop below the targeted oven draft beforegenerating the position instruction. Inferential control can be used totake into account the interplay between the various operating conditionsat various locations in the coke plant 100. For example, inferentialcontrol taking into account a requirement to always keep the oven undernegative pressure, controlling to the required optimal oven temperature,sole flue temperature, and maximum common tunnel temperature whileminimizing the oven draft is used to position the automatic uptakedamper 305. Inferential control allows the controller 370 to makepredictions based on known coking cycle characteristics and theoperating condition inputs provided by the various sensors describedabove. Another example of inferential control allows the automaticuptake dampers 305 of each oven 105 to be adjusted to maximize a controlalgorithm that results in an optimal balance among coke yield, cokequality, and power generation. Alternatively, the uptake dampers 305could be adjusted to maximize one of coke yield, coke quality, and powergeneration.

Alternatively, similar automatic draft control systems could be used toautomate the primary air dampers 195, the secondary air dampers 220,and/or the tertiary air dampers 229 in order to control the rate andlocation of combustion at various locations within an oven 105. Forexample, air could be added via an automatic secondary air damper inresponse to one or more of draft, temperature, and oxygen concentrationdetected by an appropriate sensor positioned in the sole flue 205 orappropriate sensors positioned in each of the sole flue labyrinths 205Aand 205B.

As utilized herein, the terms “approximately,” “about,” “substantially,”and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and areconsidered to be within the scope of the disclosure.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

It should be noted that the orientation of various elements may differaccording to other exemplary embodiments, and that such variations areintended to be encompassed by the present disclosure.

It is also important to note that the constructions and arrangements ofthe apparatus, systems, and methods as described and shown in thevarious exemplary embodiments are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited in the claims.For example, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of any processor method steps may be varied or re-sequenced according to alternativeembodiments. Other substitutions, modifications, changes and omissionsmay also be made in the design, operating conditions and arrangement ofthe various exemplary embodiments without departing from the scope ofthe present disclosure.

The present disclosure contemplates methods, systems and programproducts on any machine-readable media for accomplishing variousoperations. The embodiments of the present disclosure may be implementedusing existing computer processors, or by a special purpose computerprocessor for an appropriate system, incorporated for this or anotherpurpose, or by a hardwired system. Embodiments within the scope of thepresent disclosure include program products comprising machine-readablemedia for carrying or having machine-executable instructions or datastructures stored thereon. Such machine-readable media can be anyavailable media that can be accessed by a general purpose or specialpurpose computer or other machine with a processor. By way of example,such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROMor other optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to carry or storedesired program code in the form of machine-executable instructions ordata structures and which can be accessed by a general purpose orspecial purpose computer or other machine with a processor. Wheninformation is transferred or provided over a network or anothercommunications connection (either hardwired, wireless, or a combinationof hardwired or wireless) to a machine, the machine properly views theconnection as a machine-readable medium. Thus, any such connection isproperly termed a machine-readable medium. Combinations of the above arealso included within the scope of machine-readable media.Machine-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing machines to perform a certain function orgroup of functions.

What is claimed is:
 1. A method of operating a coke producing plantcomprising: providing a plurality of coke ovens to produce coke andexhaust gases; directing the exhaust gases from each coke oven to acommon tunnel; fluidly connecting a plurality of heat recovery steamgenerators to the common tunnel in parallel; operating all of the heatrecovery steam generators at a first capacity and dividing the hotexhaust gases such that a portion of the hot exhaust gases flows througheach of the heat recovery steam generators; and in a gas sharingoperating mode, stopping operation of at least one of the plurality ofheat recovery steam generators, operating at least one of the remainingplurality of heat recovery generators at a second capacity that isgreater than the first capacity, and dividing the exhaust gases amongthe remaining operating plurality of heat recovery steam generators suchthat a portion of the exhaust gases flows through each of the remainingoperating heat recovery steam generators.
 2. The method of claim 1,further comprising: maintaining operating conditions within each cokeoven at an oven draft of at least 0.1 inches of water.
 3. The method ofclaim 2, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least0.7 inches of water.
 4. The method of claim 2, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 1.0 inches of water.
 5. The methodof claim 2, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least2.0 inches of water.
 6. The method of claim 1, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 0.7 inches of water.
 7. The methodof claim 1, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least1.0 inches of water.
 8. The method of claim 1, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 2.0 inches of water.
 9. The methodof claim 1, further comprising: in a normal operating mode, maintainingoperating conditions at a location within the common tunnel at a commontunnel draft of less than 0.7 inches of water; and in the gas sharingoperating mode, maintaining operating conditions at the location withinthe common tunnel at a common tunnel draft greater than 0.7 inches ofwater.
 10. The method of claim 9, further comprising: in the normaloperating mode, maintaining operating conditions at a location withinthe common tunnel at a common tunnel draft of less than 0.6 inches ofwater; and in the gas sharing operating mode, maintaining operatingconditions at the location within the common tunnel at a common tunneldraft greater than 1.2 inches of water.
 11. The method of claim 1,further comprising: providing a plurality of crossover ducts, whereineach crossover duct is connected to one of the heat recovery steamgenerators and connected to the common tunnel at an intersection. 12.The method of claim 11, further comprising: maintaining operatingconditions at one or more intersections at an intersection draft of atleast 0.7 inches of water.
 13. The method of claim 11, furthercomprising: maintaining operating conditions at one or moreintersections at an intersection draft of at least 1.0 inches of water.14. The method of claim 11, further comprising: maintaining operatingconditions at one or more intersections at an intersection draft of atleast 2.0 inches of water.
 15. A method of operating a coke producingplant comprising: providing a plurality of coke ovens wherein each cokeoven is adapted to produce coke and exhaust gases; providing a commontunnel fluidly connected to the plurality of coke ovens and beingconfigured to receive the exhaust gases from each of the coke ovens;providing a plurality of standard heat recovery steam generators,adapted to operate at a first capacity, fluidly connected to the commontunnel, wherein the ratio of coke ovens to standard heat recovery steamgenerators is at least 2.0:1; providing a redundant heat recovery steamgenerator and fluidly connecting the redundant heat recovery steamgenerator to each of the plurality of coke ovens so that: (i) therecovery steam generators and the redundant heat recovery steamgenerator are all fluidly connected in parallel with each other; and(ii) the redundant heat recovery steam generator is adapted operate at asecond capacity, which is higher than the first capacity, receive theexhaust gases and extract heat from the exhaust gases generated by anyof the plurality of coke ovens when a capacity of at least one of thestandard heat recovery steam generators is reduced.
 16. The method ofclaim 15, further comprising simultaneously operating the plurality ofstandard heat recovery steam generators and the redundant heat recoverysteam generator during a normal operating mode of the coke producingplant.
 17. The method of claim 15, further comprising: maintainingoperating conditions of each coke oven at an oven draft of at least 0.1inches of water.
 18. The method of claim 17, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 0.7 inches of water.
 19. The methodof claim 17, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least1.0 inches of water.
 20. The method of claim 17, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 2.0 inches of water.
 21. The methodof claim 15, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least0.7 inches of water.
 22. The method of claim 15, further comprising:maintaining operating conditions at a location within the common tunnelat a common tunnel draft of at least 1.0 inches of water.
 23. The methodof claim 15, further comprising: maintaining operating conditions at alocation within the common tunnel at a common tunnel draft of at least2.0 inches of water.
 24. The method of claim 15, further comprising:providing a plurality of redundant heat recovery steam generatorsfluidly connected to each of the plurality of coke ovens.
 25. A methodof operating a coke producing plant comprising: providing a plurality ofcoke ovens, wherein each coke oven is adapted to produce coke andexhaust gases; providing a common tunnel fluidly connected to theplurality of coke ovens and being configured to receive the exhaustgases from each of the coke ovens; providing a plurality of heatrecovery steam generators that are fluidly connected in parallel witheach other; providing a plurality of crossover ducts, each crossoverduct adapted to fluidly connect the common tunnel to one of theplurality of heat recovery steam generators at an intersection; reducinga capacity of at least one of the plurality of heat recovery steamgenerators below a capacity of the remaining plurality of heat recoverysteam generators; increasing a capacity of at least one of the pluralityof heat recovery steam generators above the capacity of the at least onereduced capacity heat recovery steam generator; and controllingoperating conditions at one or more of the intersections to maintain anintersection draft of at least 0.7 inches of water.
 26. The method ofclaim 25, further comprising: controlling the operating conditions atone or more of the intersections to maintain an intersection draft of atleast 1.0 inches of water.
 27. The method of claim 25, furthercomprising: controlling the operating conditions at one or more of theintersections to maintain an intersection draft of at least 2.0 inchesof water.
 28. The method of claim 25, further comprising: controllingthe operating conditions within each coke oven to maintain an oven draftof at least 0.1 inches of water.